Adaptive Bit Rate (ABR) is a multimedia streaming technique in which multimedia content is streamed to a client in segments, typically of equal duration, that may differ from each other in their respective encoding bit rates. Typically, when requesting a segment, the client specifies an encoding bit rate from a plurality of predefined bit rates, and the server then streams the requested segment having the specified encoding bit rate to the client. ABR can be used over various communication protocols, such as Hyper-Text Transfer Protocol (HTTP) and HTTP-Secure (HTTPS).
To avoid any confusion, it is important to distinguish between “encoding bit rate” and “communication bit rate.” The term “encoding bit rate” refers to the bit rate at which the media (e.g., video) content provided to the client is encoded. Generally, a high encoding bit rate corresponds to high media quality, and vice versa. The term “communication bit rate,” on the other hand, refers to the bit rate at which the media is downloaded by the client. The communication bit rate is not necessarily related to the encoding bit rate. For example, for a given encoding bit rate, the communication bit rate may vary, depending on the conditions of the communication channel to the client. (It is noted that the present application also refers to a “streaming bit rate,” the rate at which the video is streamed from the server, which may be greater than the communication bit rate.)
Jain, A. et al., Mobile Throughput Guidance Inband Signaling Protocol, IETF Internet Draft, Sep. 7, 2015, which is incorporated herein by reference, proposes a mechanism and protocol elements that allow a cellular network to provide near real-time information on capacity available to the TCP server. This “Throughput Guidance” (TG) information would indicate the throughput estimated to be available at the radio downlink interface (between the Radio Access Network (RAN) and the mobile device (UE)). The TCP server can use this TG information to ensure high network utilization and high service delivery performance. The document describes the applicability of the proposed mechanism for video delivery over cellular networks; it also presents test results from a live operator's environment.